1. Field of the Invention
The present invention relates to an electronic ballast for a high intensity discharge lamp. More specifically, the invention relates to an electronic ballast for a high intensity discharge lamp that enables high intensity discharge lamps having different rated powers to be lit according to the rated powers.
2. Description of the Prior Art
Japanese Patent Publication H7-66864 discloses a ballast for lighting two or more fluorescent lamps having different rated powers. The ballast is so designed as to determine the rated power of a fluorescent lamp by taking advantage of the fact that different starting voltages are applied to start fluorescent lamps having different rated powers. In addition, the ballast is so designed as to supply a current according to the determined power. In other words, the ballast determines the rated powers of fluorescent lamps from the difference among the starting voltages applied to start the lamps discharging.
By contrast, even if high intensity discharge (HID) lamps have different rated powers, a nearly equal starting voltage is applied to start the HID lamps discharging. This makes it impossible to apply to the HID lamps the art disclosed by the foregoing publication.